Conventional system for preventing a wheel of a motor vehicle from locking have been known, for example, a system which controls a brake fluid pressure applied to a wheel cylinder of a brake device based on a rotation status of the wheel relative to a threshold value when the brake is operated and then the vehicle decelerates.
Further, there has been a conventional system for preventing a driving wheel of a vehicle from slipping by controlling a brake force caused by a brake fluid pressure in a wheel cylinder of a brake device of the driving wheel based on a slipping status relative to a threshold value when the vehicle starts to move and accelerates.
In these conventional systems, each of the controls of the brake fluid pressure requires an individual fluid pressure circuit in order to independently increase and decrease the brake fluid pressure. In this case, moreover, it is necessary to provide an extra solenoid device for closing a fluid supply passage communicating with the wheel cylinder of brake device for the driven wheel to make the brake act merely on the driving wheel while the driven wheel is free from the brake action. Accordingly, such a conventional system may have a problem in that the fluid pressure circuit tends to become complicated, large-sized and thus raise a manufacturing cost.